Unfortunately, you weren't kidding about this not being stable.

That being said, the backbend/bridge is a great pose, and I'd love to see a useable version. More info below in case it helps with refining this.

This is extremely susceptible to interference by basic prompts, although it plays surprisingly well with other loras (no additional distortion was obvious, and some clothing loras actually seemed to help stabilize the body shape). Also doesn't seem to like basic pony or pony realism (unsure of reasons). If it needs a specific pony subset, mention which checkpoints work in the description.

Eventually tried outright copying your sample image's prompts with standard pony 6 XL. While still rough, that particular seed looked better than the batch of 49 I ran after with the same prompt, but at this point I'm gonna say that I definitely can't get this to produce anything remotely useable with it. It isn't pure noise, so I won't call it outright incompatible, but it isn't close to being useable with it either.

Ran a bunch of batches of 4 and a few batches of 49, 0 of 450ish were good enough to inpaint (the small batches that had a correctly shaped pose and looked promising enough to try a larger batch appear to have just been flukes).